1. Field of the Invention
This invention relates to ammunition feed systems for firearms, particularly to a magazine adapter used with a twin-drum magazine to convert the dual-feed arrangement of rounds created thereby into a single-feed arrangement that will allow dual-feed twin-drum magazine use with a wider variety of automatic and semi-automatic firearms, including rifles and many pistols of differing caliber that require a single-feed system. The capability of converting rounds from a dual-feed twin-drum magazine into a single-feed arrangement was unknown in the prior art until developed by the inventor herein. In the prior art, a dual-feed twin-drum magazine created a double-column arrangement of rounds in the feed tower connected between it and the automatic or semi-automatic firearm, with the rounds in each column positioned within the tower offset from those in the other column by a measurement equaling approximately one-half of a round's diameter. Since the width dimension of the tower remained uniform from top-to-bottom to accommodate the two side-by-side columns of stacked rounds, they remained in their double-column arrangement until they reached the tower's centered feed opening, after which the topmost round in the feed tower (the one positioned closest to the feed opening) would first exit the tower through the feed opening, followed by the topmost round in the other column which then assumed the position closest round to the feed opening, with the remaining rounds alternatively exiting the centered feed opening one-at-a-time, first from one column, and then from the other column. As a result of such a dual-feed arrangement of rounds close to the tower's feed opening and the extra width dimension in the top portion of the tower needed to accommodate both columns, firearms requiring a single-feed arrangement were unable to use dual-feed twin-drum magazines and could not benefit from the increased firepower advantage they offered. Also as a part of prior art feed towers connected to a dual-feed twin-drum magazines, and to prevent the firearm from loading dummy rounds needed to advance ammunition to the feed opening, a rigid/fixed link was provided between the dummy cartridge that would become the lead cartridge when the magazine was completely unloaded and the cartridge immediately behind it in the same column.
In contrast, the interior top portion of the present invention single-feed magazine adapter close to its feed opening is narrower than the prior art towers used with dual-feed twin-drum magazines, and each opposed interior side of the present invention adapter near its feed opening is configured to provide a gentle inward taper that creates minimal void space for the conversion of rounds from a dual-feed arrangement to a single-feed arrangement, while exterior tapering in the top portion of the present invention adapter is configured for connection to firearms requiring a single-feed system. The height dimension of the present invention adapter is not critical. In combination with an interlocking/expandable and flexible link between two of the three specialty rounds having ammunition in front of them and numerous dummy/filler rounds behind them, which are initially positioned within one of the drum magazines, the link and interior tapering create a pendulum movement in rounds approaching the adapter's feed opening. The pendulum movement comprises a slight and brief separation of the linked specialty rounds each time a round leaves the feed opening that causes needed rotation and movement of the ammunition ahead of them to urge the ammunition close to the feed opening into a single-feed arrangement, after which the linked specialty rounds move back together, with the pendulum movement repeating after each round exits the feed opening and the next round in single-feed positioning at the top of the other column (now in single-feed positioning) moves closer to the feed opening for next use by the firearm attached to the adapter. The pendulum movement continues until all rounds ahead of the three specialty rounds have been fired and the three specialty rounds come to a stop next to the adapter's feed opening. The flexible link used in the present invention may be a washer or ring, but is not limited thereto. Furthermore, the present invention single-feed magazine adapter can be manufactured using multiple-piece construction and assembly, or manufactured as a single-piece unit via molded construction. In addition, the present invention adapter can be manufactured for retrofit attachment to an existing dual-feed twin-drum magazine (to replace its previously-used feed tower), or the present invention adapter may become associated with a new dual-feed twin-drum magazine during manufacture. An important advantage of present invention dual-feed twin-drum magazine adapter use is that all automatic and semi-automatic handguns requiring a single-feed system will be able to utilize the dual-feed and higher capacity twin-drum magazines, giving them increased firepower. Additional advantages include low present invention manufacturing cost, ease of use, easy attachment to and removal from the firearm during reloading, and preservation of pre-load tension for easier reloading once all rounds ahead of the three specialty rounds have been fired and the three specialty rounds come to a stop next to the adapter's feed opening.
2. Description of Related Art
In both military and non-military applications, increased fire power for automatic and semi-automatic weapons can provide users with increased security and other advantages. However, in the prior art high-capacity twin-drum magazines provide only a dual-feed arrangement for ammunition, while some firearms (including many current inventory automatic and semi-automatic pistols manufactured by Glock, Baretta, Sig Sauer, Heckler Koch, Ruger, and Springfield) only accept a single-feed arrangement of rounds, and until development of the present invention single-feed magazine adapter have been excluded from increased fire power advantage. An important advancement toward increased fire power was provided about 35-40 years ago by the twin-drum magazine disclosed in U.S. Pat. No. 4,658,700 to Sullivan (1987), which offered a fire power advantage over previous inventions by allowing the use of a magazine containing one hundred ammunition rounds instead of a mere thirty rounds. However, there remains room for improvement in the industry, in part due to the limitation of Sullivan twin-drum magazine to a dual-feed arrangement of rounds. The present invention provides such improvement, since when it is used with the dual-feed twin-drum magazine disclosed in the above-mentioned Sullivan patent, which is currently sold by The Beta Company, or used with a dual-feed twin-drum magazine from any other manufacturer, the present invention adapter converts the dual-feed arrangement of cartridges into a single-feed arrangement without modification of the firearm, allowing use of dual-feed twin-drum magazines with a wider variety of automatic and semi-automatic firearms that require a single-feed system.
The above-mentioned Sullivan invention is thought to be the closest in concept to the present invention, however, there are important structural differences between the present invention and the Sullivan invention. The abstract of the Sullivan disclosure states that it relates to gun magazines having one or two generally-cylindrical drums, with the single-drum magazine providing a single-feed arrangement of rounds and the twin-drum magazine providing a dual-feed arrangement of rounds. In the Sullivan twin-drum magazine, cartridges are positioned in each drum within two concentric rings and advanced by a spring until they reach a cam blade, which forces the cartridges from that drum into a stacked single-column arrangement that is staggered from the stacking in the adjacent column by approximately the width dimension of one-half a round. FIG. 8 of the Sullivan disclosure shows the cartridges in a single drum moving in a single column toward an exit passage, while FIG. 4 shows the cartridges in two drums moving in a column toward the same exit passage. Sullivan does not disclose any adaptation of its twin-drum magazine to a single-feed arrangement, instead providing two independent drum magazines, one with a single-feed arrangement and the other with a dual-feed arrangement. FIGS. 4 and 8 in the Sullivan disclosure also both show the top portion of the ‘exit passage’ (referencing the feed tower positioned between a drum or twin-drums and a firearm) adjacent to feed throat 29 being non-tapering, instead having the topmost part thereof on both sides sharply bent inwardly to form the feed opening. In contrast, the present invention single-feed magazine adapter has gentle inward-tapering on both of its opposing sides proximate to the firing position, which in combination with a flexible interlocking/expandable link positioned between the top-most or lead specialty round and the second (referenced from the feed opening) specialty round behind it when all ammunition has exited the feed opening, or in the alternative between the lead specialty round and the third (referenced from the feed opening) specialty round behind it, the tapering structure and link create a pendulum movement of rounds within the adapter that enables a successful conversion of the rounds ahead of the three specialty rounds into a single-feed arrangement as they come close to the firing position. Rounds in the present invention adapter remain in a staggered dual-feed arrangement until the tapering begins. In contrast, as shown in FIG. 3 of the Sullivan disclosure, when the twin drums in the Sullivan magazine are completely unloaded, the two filler rounds attached together by a rigid/fixed connector (that advance to the feed opening immediately behind the ammunition) will become positioned one-above-the-other in one of the dual-feed columns adjacent to the feed opening (and the lead filler round in the Sullivan invention can never be linked to the third round behind it, contrary to such positioning that is possible in the present invention adapter. Also, the interlocking/expandable link used in the present invention may be a washer or ring, but is not limited thereto, as long as it allows the specialty rounds it links together to experience the needed pendulum movement of becoming slightly and briefly separated from one another when each ammunition round exits the feed opening, and then come back together once the next round behind it in a single-feed column has advanced to the firing position. The same pendulum motion also aids reloading of the reusable present invention single-feed magazine adapter.